Download The Earth`s Magnetic Field

The Earth's Magnetic Field
Objective:
The object of this lab is to measure the magnitude of the earth's total magnetic field in Orlando
Florida!
Equipment:
Tangent Galvanometer, digital multimeter DMM, current limiting resistor, power supply and
banana plug wires
Theory:
The magnetic field produced by a circular loop of wire is given by:
B =N
oi
2R
where 0= 1.26x10 T m/A, N is the # of loops, i is the current in the loop, and R is the radius of the loop.
-6
.
The total field, then, will be the vector sum of the Earth's magnetic field and the magnet's field,
and in the case when both fields are perpendicular to each other, it will be:
Tan ө = B/Be
Where ө is the angle between the total field and the Earth's field can be measured by using a
compass, whose needle always aligns itself along the total magnetic field at the point where it is
placed. Be is the magnetic field of the earth.
Procedure:
1. Wire the tangent galvanometer, the current limiting resistor, the DMM , and the power supply
together in a series circuit. (See fig. 1 above) The tangent galvanometer has three places to
connect wires. Where the wires are connected determines how many loops the current must pass
through. Wire the circuit so that the current passes through 5 loops. Have your professor
approve your circuit before plugging in the power supply.
2. Align the tangent galvanometer coil so that it is parallel to the to the earth's magnetic field as
shown below
Do this by rotating the dip needle so that it is horizontal and can act as a compass. The coil of the
tangent galvanometer should be in line with the "compass" needle which points north-south.
3. Measure three different values for the angle өby varying the current input. Record the angle
and the current. Calculate the magnetic field using the first equation and using the second
equation calculate BE.
4. Repeat step three using 10 loops and again for 15 loops of current carrying wire, for a total of
nine trials. Calculate the average horizontal field from these data.
5. Measure the dip angle of the total field with the dip needle. Make sure that the power supply
to the tangent galvanometer is off. From this angle, calculate the total field.
Questions/Conclusions:
1. Compare the value of the total field found in this experiment to a standard value for the
magnetic field of earth in a place closer to Orlando Florida.
2. Calculate the total resistance of 15 loops of copper wire on the galvanometer if the wire is 1
mm in diameter and the loops are 20 cm in diameter. (The resistively of copper is 1.69 x 10-8
ohmmeter )
3. Why was the current limiting resistor needed in the circuit? (See previous question)